1. Field of the Invention
The present invention relates to a device for detecting the manner in which an automobile is driven in order to control the steering characteristics of a power steering apparatus, the height of the automobile etc.
2. Discussion of Background
Previously, the traveling conditions of the automobile were generally detected on the basis of the automobile speed. Then, the detected traveling conditions were used for controlling, for example, the assist force of a power steering apparatus so that this force becomes large in a range of lower velocities but small in a range of higher velocities. For instance, as disclosed in U.S. Pat. No. 4,593,358 patented to S. Takeshima et al., a well-known power steering apparatus is arranged such that a plurality of control characteristics between the automobile speed and a rotational frequency of an oil pump are prepared,, and one of these control characteristics is selected, depending on the conditions of streets of cities or towns and mountain roads This type of apparatus is capable of varying the characteristics existing between manual steering torque and steering output torque by changing the assist force in accordance with not only the difference between the automobile speeds but also the difference between the road conditions.
However, there arise some problems in which the traveling condition of the automobile varies according to a feeling and a character of the driver in addition to the automobile speed and the road conditions, i.e., the traveling condition depends on whether the driver drives the car aggressively or moderately. This steering force which is suited to the operating condition determined by the driver cannot be obtained in the prior art.
In order to obviate the above-described problems, a method of determining the steering force taking the driving conditions as well as the road conditions into consideration has been proposed, which is disclosed in U.S. patent application Ser. No. 06/946,050, now U.S. Pat. No. 4,773,498, assigned to the assignees of the present invention. In the previously proposed invention, however, a driving condition index which exhibits the driving condition is calculated in the form of a numerical value on the basis of the automobile speed, and hence the steering force often varies in proportion to frequent changes in automobile speed according to traffic situations in which the automobile travels As a result, an unnatural feeling is imparted to the driver.
In order to improve driving feeling, the assignee of this invention have also proposed another method, which is disclosed in U.S. patent application Ser. No. 07/098,185. In this method, even if the driving condition index decreasing radically, the steering force is decreased at a constant rate so as to prevent a sudden decrease in the steering force, which gives an abnormal feeling to the driver In this proposed invention, however, the rated decrease of the steering force is set at a constant value. If the rate of decrease is set at a constant value which gives good feeling to the driver at the low speed driving, the driver feels that it takes too long to decrease the steering force during high speed driving, at which time the driver is under duress. Therefore, the slow decrease of the steering force gives an incompatible feeling to the driver at the high speed driving. The same problems arise when either the height of the automobile or the characteristic of the suspension is controlled depending on the driving condition of the driver.